(a) Field of the Invention
The present invention relates to a multilayer wiring board for mounting a semiconductor device, particularly a multilayer wiring board which has a multi-bonding-deck cavity (multi-pad-level cavity) for housing a semiconductor device and connecting the semiconductor device with interconnect leads, and is used for mounting semiconductor devices. The present invention further relates to a method of producing the multilayer wiring board for mounting a semiconductor device.
(b) Description of the Related Art
With the recent advance of electronic instruments, the requirements of wiring boards for high density wiring has become increasingly strict. Particularly, in multilayer wiring boards used in semiconductor packages of pin grid array (PGA) type, ball grid array (BGA) type, etc., the increase of output signal wires has been accompanied by an increase of the number of wire bonding pads for making connection with semiconductor devices. This requires complicated shape-processing, such as formation of multi-bonding-deck cavities.
Examples of bonding materials which has been used for multi-layering the wiring boards for mounting semiconductor having multi-bonding-deck cavities, include prepregs reinforced by glass fiber, polyimide resin adhesives, epoxy resin adhesives and rubber-epoxy resin adhesives.
When the prepregs are used for the production of wiring boards requiring complicated shape-processing, such as formation of cavities, resin powder is scattered on machining for cutting out cavity portions and adheres to wire bonding pads at the time of lamination, to cause occasional connection errors in wire bonding process.
Further, when prepregs are used, there arises difficulty in controlling the flowability of resins during lamination with heat and pressure. Resins of high flowability increase exudation into cavities to coat wire bonding pads with the exudate and increase connection errors. Resins of low flowability reduce exudation into cavities, but tend to form voids around internal circuit conductors to deteriorate insulation reliability. Therefore, the use of prepregs has the disadvantage of low production efficiency due to low yield. To solve these problems, such as low processability, there has recently occurred increasing demands to use as interlaminar adhesive films which do not contain woven or non-woven cloth reinforcing materials and is easy to control flowability and generates no cutting chips or powder.
However, it is not that any adhesive film can be used for the production of multilayer wiring boards. Due to the larger content of high-molecular weight resins as compared with prepregs, adhesive films make it easy to control the flow of resins at the time of lamination with heat and pressure, namely to reduce the exudation of resins into cavities and to prevent the formation of voids at the sides of patterned copper foil which forms internal circuits. However, to ensure industrially stable yield, it is necessary to understand the relationship between the physical properties and processability of adhesive films, and there are demands for adhesive films suitable for production facilities and means of controlling their physical properties.
None of the adhesive films of prior art have a processability enough for formation of complicated structures, particularly such a stable processability as not to cause scatter in the amount of resin exudation into cavities during lamination with heat and pressure.
When polyimide or epoxy resin adhesives are used as adhesive films in the production of the recent multilayer wiring boards of high wiring density, it is impossible to improve soldering heat resistance and moisture resistance to a degree sufficient for practical uses.
Also, multilayer wiring boards which are produced by using the rubber-epoxy resin adhesives conventionally used in flexible wiring boards are poor not only in soldering heat resistance and moisture resistance, but also in connection reliability, and are inapplicable for practical uses.